The present invention relates generally to cold frames. More specifically, the present invention relates to devices that allow the user to cover and uncover a cold frame at will.
A cold frame is a lightweight enclosure that provides covering for plants and seedlings, whether planted in flowerpots or trays or in the earth enclosed by the cold frame. Typically, a cold frame comprises a framework and a covering. The framework can be made of metal, wood or plastic; and the covering is typically made of plastic sheeting (e.g., transparent polyethylene). Invariably, the covering is light-transmitting although not necessarily light transparent and is most often “fixed”; that is, it remains in place and is not easily openable or removable. For ventilation, holes can be cut in the plastic or the sides can be lifted.
The purpose of the cold frame is to protect the plants and seedlings from the extremes of the environment: cold, wind, or excessive amounts of rain or “hard” rains. However, cold frames can also cause problems for growing plants. They trap heat, for example. Also, because plants naturally grow toward the light—a tendency known as phototropism—and because cold frame coverings invariably attenuate the light, plants in cold frames can tend to be spindly.
Ideally, cold frames should have a cover that can be opened when the weather is clear and warm, and that can be closed on nights when the temperature is expected to drop to unacceptably low levels, or on days when it will rain excessively or rain hard, or when too much heat has built up in the cold frame. Such a cover would not only help to regulate the temperature within the cold frame, but would reduce watering costs and make plants healthier, thicker and fuller.
Cold frames can be uncovered and recovered manually, of course, but the cost, time and labor associated with uncovering and recovering manually makes it impractical to do so frequently. For example, it may take a team of two to six men several hours to cover or uncover a typical cold frame. Some commercial farms may have hundreds of cold frames at a single growing site. Moreover, when a cold frame is uncovered and the plastic is removed, the plastic often is abraded, pierced, and/or torn such that it cannot be used again. Moreover, it is usually dirty and wrinkled making it unfit for reuse and very difficult to fold or roll for storage.
Accordingly, every year, millions of pounds of plastic is purchased at enormous expense to cover cold frames. Once the plastic has been used (e.g., one growing season for 4 mil polyethylene), it must be disposed of in landfills or recycled. The plastic is enormously bulky and many landfills are reluctant, or refuse, to accept it. Furthermore, when the plastic is recycled, it cannot be made into covering again because the recycled plastic does not have the required transparency and toughness.
In short, it is simply impractical to cover and uncover the cold frames. Leaving the cold frame covered when no cover is needed, however, can be harmful both to the plants (overheating) and to the plastic as well. Polyethylene and many other plastics deteriorate when exposed to UV radiation. Having the covering exposed to sunlight unnecessarily, for example on warm fall, spring, or summer days, needlessly degrades the covering. Accordingly, the need exists for a system that quickly, efficiently, and reliably uncovers and recovers a cold frame without damaging the plastic covering.
Moreover, a system for uncovering a cold frame must be simple structurally so that it is not cost prohibitive. It must be easy to use so that cold frames can be uncovered and covered quickly and without special training. Commercial growers may use dozens or hundreds of cold frames. If the closure mechanism is too complicated or slow, operating it may require extensive manpower or time or both. Finally, the covering mechanism must accommodate the characteristics of plastic. These characteristics include (1) the tendency to “bathtub” or collect water where the plastic sags, (2) the tendency to catch the wind and (3) the tendency to tear or rip if mishandled.
However, the advantages of a system that can meet this requirement are considerable. An inexpensive, easy-to-use and reliable system for covering and uncovering the cold frame can make growing of plants much easier and result in higher quality plants, better yields and lower costs. Moreover, such a system is not limited to use on small plants. Cold frames can also be constructed over trees in an orchard. For example, cherry trees, which are extremely sensitive to rain during the roughly two-week period before harvesting, could be covered with cold frames during that specific period of time, and uncovered the rest of the time. Temporary structures for out-of-door events can also benefit from such a mechanism.
There remains a need for a covering mechanism for cold frames that operates easily and simply and does not add unduly to the overall cost of cold frame construction.